1. Field of the Invention
The present invention relates to a display of a liquid crystal, CRT, or the like and, more particularly, to an image display having the function of enlarging an image by increasing the number of pixels of an input image and displaying the image with higher resolution.
2. Description of the Related Art
In recent years, the resolution of various image displays and displays having a larger number of pixels have been developed. The pixel is defined here as a minimum unit of expressing a color. In the case of using three primary colors of R (red), G (green) and B (blue), a pixel consists of a set of three continuous dots of R, G, and B arranged in a column or a row. For example, in a liquid crystal display, the number of pixels has been increased from VGA (640 pixels in the horizontal directionxc3x97480 pixels in the vertical direction) to XGA (1024 pixels in the horizontal directionxc3x97768 pixels in the vertical direction). Further, SXGA (1280 pixels in the horizontal directionxc3x971024 pixels in the vertical direction) is commercially available.
It is accordingly becoming more and more necessary to enlarge an input image of a low resolution of an NTSC signal (corresponding to pixels of 640 in the horizontal directionxc3x97500 in the vertical direction), a signal for a VGA liquid crystal display, or the like by increasing the number of pixels of the image so as to display an image of the increased number of pixels on a high-resolution screen. In this case, data of a pixel interpolated between pixels in an original image on a display screen is newly generated as an interpolation value. Proposed methods of obtaining an interpolation value include a method of using the same data as that of one of neighboring pixels in an original image and a method of obtaining an intermediate value of two neighboring pixels in an original image. Generally, the latter method of obtaining an intermediate value, that is, a linear interpolation process for obtaining a value on a straight line connecting two neighboring pixels is used.
FIG. 5 is a conceptual chart showing an algorithm of a linear interpolation process. In the chart, a case where the scaling factor of 2 of inserting one interpolation pixel between neighboring two pixels in an original image is shown in the range from a pixel 0 to pixel 3. The brightness will be described as data K of an image. The brightness values of interpolated pixels are calculated as intermediate values (K1+K2)/2, (K2+K3)/2 and (K3+K4)/2 on a straight line connecting K0 and K1, a straight line connecting K1 and K2 and a straight line connecting K2 and K3, respectively. A case of interpolating two or more pixels between neighboring pixels in an original image is quite similar. Values on a straight line connecting brightness data on both sides are used as interpolation values.
The conventional interpolating method is characterized in that a change in gradation of an original image is subjected to an enlarging process and an image with a smooth gradation change is obtained also on a high resolution display screen. On the other hand, an intermediate value is inserted even in a sharp edge portion in an original image, so that there is a problem such that the outline is blurred in the enlarged image on the display screen.
It is an object of the invention to solve the problem and to provide an image display comprising means for selecting an interpolation value so that an outline is not blurred in an enlarged image and means for displaying the enlarged image.
In order to achieve the object, an image display according to the invention comprises: means for selecting an interpolation value Zm as data of the mth (m denotes a natural number equal to or smaller than n) interpolation pixel from a pixel 1 within the range from Xm to Ym which are obtained by the following equations, in the case where n (n is a natural number) pixels are interpolated between two neighboring pixels 1 and 2 in an input image signal,
Xm=K1+m(K1xe2x88x92K0)/(n+1)
Ym=K2+(n+1xe2x88x92m)(K2xe2x88x92K3)/(n+1)
where, data of a pixel 0 adjacent to the pixel 1 on the side opposite to the pixel 2 is K0, data of the pixel 1 is K1, data of the pixel 2 is K2, and data of a pixel 3 adjacent to the pixel 2 on the side opposite to the pixel 1 is K3; and
means for outputting the interpolation value as data of a corresponding pixel on a display screen.
In the image display according to the invention, the value Zm is calculated by the following equation.
Zm=(Xm+Ym)/2
By those means, a clear image can be obtained while preventing the outline of an edge portion in an original image from being blurred in an enlarged image on a display screen.
The image display according to the invention further comprises means for adopting one of the data K1 and K2, which is closer to the value Zm as an interpolation value when the value Zm is out of the range from the data K1 to the data K2.
Consequently, an excessive correction, that is, what is called an overshoot occurring in the image display according to the invention can be prevented and insufficiency of the texture due to excessive sharpness of the outline can be compensated.